01 Osborn, A. F. (1963). Applied Imagination, 3rd ed. Scribner.
02 It can be useful to do a “Yes, and …” warm-up before this exercise; or remind people of the concept if they know it already. See #TiSDD 10.7.1, Warm-ups.
03 Nemeth, C. J., & Nemeth-Brown, B. (2003). “Better than Individuals? The Potential Benefits of Dissent and Diversity for Group Creativity.” In P. Paulus and B. Nijstad (eds.), Group Creativity (pp. 63-84). Oxford University Press.
Brainstorming  (the term is often misused to describe all kinds of idea generation processes) is a specific group exercise which uses simple rules to help participants stay in a productive, nonjudgmental, highly divergent mode while producing many ideas.
Participants call out ideas which are written down on a board by a facilitator or scribe. This generates a pile of ideas quickly. Use brainstorming to find a starting point (or several starting points) for your work, to get to grips with the theme as a group, to widen the number of alternatives, or when you get stuck and need options.
- Make sure you are using the right method. Brainstorming will help the group quickly understand what the others are thinking and what the mood is around the subject, like “testing the water.” It’s also great when the group needs energy. If you want to generate more diverse ideas, and empower the less assertive group members, a quieter method like brainwriting might be better.
- Look at your starting point for ideation and consider if and how you will bring previous knowledge into the room (for example, as a research wall or as key insights).
- Invite the right people to work beside your core team for the exercise (this might include people who know the background, people with no preconceptions, experts, representatives of the implementation team, people who will deliver the service, users, management, etc.).
- Prepare your group with information and arrange them comfortably. They should all be able to see the board. The scribe or scribes will need good pens and a clear, fast hand.
- Remind the group of Osborn’s rules that they (a) refrain from criticism, (b) are open to wild or unusual ideas, (c) focus on quantity of ideas, and (d) build on the ideas of others. 
- Show the theme or key question on a poster or projector. (You might do an engaging warm-up after this to distract the participants for a few minutes.)
- In brainstorming, ask the group to shout out their ideas or answers. Write their words legibly on the board.
- When all ideas are on display you can group them under whatever criteria the group prefer, discuss them, and/or begin a selection technique.